Emissions Regulations

The reduction of NOx and particulate matter (PM) has been central to the U.S. Environmental Protection Agency's (EPA) strategy for cleaner air. Since the passing of the Clean Air Act in the 1970s, the EPA has made steps to lower emissions of NOx, PM and other pollutants from road vehicles, electric utilities and off-road equipment, and periodically reviews national air quality standards.

The EPA has a specific responsibility under the Clean Air Act to manage and enforce emissions limits at a federal level. It sets the limits for emissions standards for diesel engines and takes actions against manufacturers who do not meet the standards. It also takes an active interest in the technology choices that are made by the manufacturers (although it cannot express a preference) and assesses their current progress.

Heavy-duty trucks

EPA standards for emissions from heavy-duty diesel trucks have been lowered dramatically since 2001. The EPA guidelines stipulated in 2001 that models manufactured from January 2010 must reduce PM emissions to 0.01 per brake horsepower hour (g/bhp-hr) and NOx emissions to 0.20 g/bhp-hr. A 'phase-in' period allowed NOx emissions of 1.2 g/bhp-hr by 2007. The EPA implemented a bank and trade system for NOx, which meant manufacturers who exceeded the requirements before 2010 (such as Cummins and Navistar) could accrue NOx credits which could be used to sell models producing emissions above the standard after the deadline. There was no banking and trading of PM emissions.

Off-road vehicles

In 2004, the EPA issued its final program to reduce emissions from off-road diesel engines, to be phased-in from 2008 to 2015. The Tier 4 off-road rule established new emissions standards and test procedures, and led to the implementation of Selective Catalytic Reduction (SCR) technology by a number of manufacturers. The exhaust standards require emissions of PM and NOx be further reduced by about 90% from Tier 1-3 standards.

Beginning in 2008, the new Tier 4 Interim engine standards for power categories of engines from under 25 hp to above 750 hp have been phased in. Tier 4 Final standards will be implemented for all engine power categories by 2015. Manufacturers can use the banking and trading program for Tier 4 engines up to 75hp.

Each of the major off-road engine manufacturers has confirmed the use of SCR for engines above 75 hp in their product range for Tier 4 Final.

Cars, pickup trucks and SUVs

The Clean Air Act first set out emissions rules for cars as part of a set of amendments in 1990 (Tier 1). Tier 2 standards were adopted in December 1999, with an implementation schedule of 2004 to 2009. Under Tier 2 federal regulations, emissions limits were made more stringent and the same emission standards were applied to all non-commercial vehicles under 10,000 lbs and commercial vehicles under 8,500 lbs. This meant passenger cars, pickup trucks and SUVs all become subject to the same rules and, because the standards are expressed in terms of emissions per mile, larger vehicles require more advanced engine and aftertreatment. Tier 2 limits the average NOx emissions of all vehicles sold by a manufacturer to 0.07 grams per vehicle mile (g/m).

American Petroleum Institute

The American Petroleum Institute (API) runs a voluntary program for certifying DEF producers and distributors through its Diesel Exhaust Fluid Certification Program. Suppliers who have been approved by the API display its logo on their DEF products, guaranteeing the quality of your purchase and its suitability for proper SCR operation. API takes random samples in the market to ensure DEF quality.

ISO standard

The production, handling and transportation of Diesel Exhaust Fluid (DEF) are governed by the ISO 22241 standard. The standard covers five main points:

Urea concentration: DEF must have a urea concentration of 32.5% by weight. This concentration was selected because it is has the lowest freezing temperature, 12°F (-11°C).

Contamination: Contaminated fluid can damage SCR injectors and catalysts, resulting in system malfunction or failure. Therefore, the maximum level of impurities permitted in DEF, such as calcium and various metals such as iron, copper, zinc and aluminum, are clearly specified. There limits are set very low. For example, a spoon of table salt in a DEF tote would push the sodium content far above the ISO 22241 limit of 0.5 ppm.

Quality: ISO 22241 excludes the use of urea granules used as fertilizer in agriculture, and requires water purified by distillation or de-ionization.

Materials: Only certain materials are permitted for the storage and handling of DEF. DEF is corrosive to many materials, including carbon steel, copper and aluminum, which cannot be used. The main risk of using incorrect materials with DEF is that the DEF will be contaminated by the material, resulting in damage or failure of the SCR system on your truck.

Handling guidelines: Guidelines require manufacturers to follow clear procedures for the manufacture and distribution of DEF, ensuring that the product you use meets the the requirements of vehicle manufacturers.

The ISO standards are available for purchase for a small fee from the ISO website.